Endoscopic optical and optoelectronic sensors comprise CCD (Charge-Coupled Device)—or CMOS (Complementary Metal Oxide Semiconductor)—modules. The requirements regarding the restricted dimensions of endoscopic instruments can make it difficult to provide the image data processing units and control units for these sensors at the distal end of the endoscopic instrument. Therefore, data transmission elements are provided which transmit the image data from the optical sensors to a supply unit and vice versa transmit control signals and driving clock cycles from the supply unit to the optical sensor.
For the data transmission of analog video signals and driver clocks having a relatively high frequency, coaxial conductors with a length of several meters have been typically used. The use of coaxial conductors is common for frequencies of more than one Megahertz (MHz), since they provide a low signal attenuation and are typically free of crosstalk at high frequencies. The data transmission systems for endoscopic optical sensors, i.e. camera or video modules, which transmit image data in a PAL- or NTSC-standard format, typically comprise a plurality of coaxial conductors for the image data and the driver clocks at a high frequency and further single elements for a voltage supply, a shutter signal or driver clocks at a low frequency.
Examples for endoscopic systems are shown in documents U.S. Pat. No. 6,007,480 and U.S. Pat. No. 5,058,568.
In the field of endoscopic optical sensors the demands regarding image quality and image resolution have continuously increased. In the same manner the bandwidth required for the required transmission of digital data increases. Parallel interfaces are difficult to implement, since they require many connections and have a rather high power demand. The available space and power consumption, however, are typically parameters that may be critical in endoscopic applications and should be kept small. Therefore, there is a demand for serial interfaces having a wide bandwidth for the transmission of analog and digital data.
It has been suggested for new endoscopic optical sensors to convert the image data signal of the optical sensor into a differential serial LVDS (Low Voltage Differential Signaling)-Signal in order to use this interface standard for transmitting image data at high speeds. Converting the image data, however, requires a further converter element which itself requires a certain space. Twisted pair cables are used as data transmission elements. Twisted pair cables are cables that have twisted pairs of strands. The twisted pairs of strands are provided with symmetrical signals in order to evaluate a difference between the signals on both strands at the proximal end of the data transmission element, e.g. using differential amplifier. Typically, the signal applied at the distal end may thus be reconstructed in an optimal manner at the proximal side of the receiver.
Examples for twisted pair cables can be found, e.g., in documents EP 0 819 311 B1 and EP 0 946 951 B1.
However, twisted pair cables have a relatively large diameter due to the twisting of the strands in order to have a sufficiently low signal attenuation considering the required length of the cable and the transmission bandwidth. This would lead to an increased diameter of the endoscopic instrument, even though the diameter should be as small as possible when using the endoscopic instrument in a procedure involving a human being.
Optical sensors having a high resolution are increasingly available in large numbers for consumers, in particular in the field of telecommunications. These sensors are used, e.g., in cellular telephones or digital cameras. These optical sensors may use the so-called MIPI CSI-2 (Camera Serial Interface)-standard in an increasing manner. An example is provided in document U.S. Pat. No. 7,899,948.
The MIPI CSI-2-standard defines a serial, fast and cost efficient interface between a peripheral image module and a mobile device with small dimensions. In particular, it is embodied as a serial interface having a high bandwidth for the transmission of image and video data over small distances of less than 30 cm (approx. 11.8 in) within a mobile consumer device.
Using miniaturized CMOS-sensors that are designed and available in large numbers for the field of telecommunications can be interesting also in the field of endoscopic instruments. Today, proprietary solutions are developed which come at a significant cost. When using the image sensors that are known from telecommunications, it would be necessary to use the MIPI CSI-2 interface as well. In order to provide the data transmission, solutions in the field of communications use flexible printed circuit boards or the previously mentioned twisted pair cables, which does not pose notable problems due to the short cable lengths in cellular devices and the resulting attenuation.
In endoscopic applications the transmission paths are typically much longer, necessitating larger diameters of cables in order to maintain a small attenuation. However, the increased diameter may not to be acceptable for the field of endoscopy. If a solution to this problem could be found, significant economic advantages could be achieved and the quality of the image transmission could be significantly increased.
It is an object of the present invention to provide an improved endoscopic instrument. It is a further object of the present invention to provide a solution for using the image sensors known from the field of telecommunications and their digital signal interfaces also in the field of endoscopy while considering the required dimensions of the instruments and the diameters of the cables.